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Core Java Programming language Theory part only
What is object oriented programming language discuss the feature of object
oriented programming in respect of java.
Object oriented programming is those type of programming in which methods and
instance variable allocate distinct memory in different location and at the time of executionmake a link between them to create a complete object, which is the basic component of the
object oriented programming. Methods allocates there respective memory at the time of
class declaration and instance variable allocates there memory at the time of object
creation at execution time. After allocation of memory by instance variable a binding
process is performed between methods and instance variable after that a complete object is
created which is the basic component of the object oriented programming.
Object are that type of element which can be uniquely identified using some identifying
properties. Alternately we can say that Object is that type of element which can be
distinguished from other element.
It is also possible to say that class type variable is called object every object must have
some identifying properties to uniquely identify a particular object. The identifying
properties are called instance variable in java. So we can say that object are the
encapsulated form of methods and instance variable. Every object must have some function
to perform task. The functions present in object are called methods in java. Finally we can
say that object are the encapsulated form of instance variable and there associated methods.
The methods present in object are common for a set of object of same type. So, methods arecreated a single copy for a set of object, and they are linked with a set of instance variable.
After creating object .instance variable are distinct for all the object and they are used to
identify a particular object. In java four visibilities are present to provide to access right of
instance variable and methods. The visibilities are as:-
Visibility
Private
Default /Friendly
Protected
Public
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1. Private :Private visibilities specify that this section can not be access directly from the outside of the object but can be access from any where of object. That means, private section
can be access from public, friendly and protected section of the object .So finally we can say
that private section is visible in a single object at a time. Private section is not inheritable.That means function and variable present in the private section
2. Default / Friendly :The default visibility is friendly in java. The default section can beaccess directly from the out side of the object. That means the default section can be access
in entire program of a particular package (Collection of related class). Default section can
be inherited into the subclass. That means variable and function present in the default
section. Default section can be override and overwrite in the subclass default section can
contains instance variable as well as methods.
3. Protected :The protected section can also be access directly from the out side of theobject. That means the protected is visible in entire program in a particular package same
as default. We know that the default section can not be access in another package but
protected section can be access other package in subclass. protected section can not be
access in non subclass in other package protected section can contains methods as well as
instance variable protected can be inherit into sub class and the method and instance
variable can be overwrite and override in the subclass . To protect overwriting and
overriding the final keyboard are used before the visibility of function and variable.
4. Public : The most visibility in java program is public. The public visibility specifies that thissection can be access from any where in java programming. Public section can directly
access from out side of object. That means public section is visible in the entire program in
a particular package. Public section can also be visible in subclass as well as in non
subclass in other package. Public section can be inheriting subclass and can be modified as
the requirement of the user.
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Core Java Programming language Theory part only
Feature of object oriented programming in respect of JAVA
Encapsulation or Abstraction.
Compiled and interpreted.A.P.I(Application program interface ).
Simple secured and robust.
Platform independence.
Generic programming.
Class and object.
Multithreading.
Polymorphism.Distributed.
Inheritance.
Constructor.
Exception.
Applet.
Interface.
Dynamic Package..
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The common name of a set of object is called class. It is also possible to say that class is the
blue print or logical design and imaginary design of object. Alternately we can say that
class is users define data type. Which is used to create new data type by encapsulating
standard data type or other user define data type with there associated member function(methods) in a single unit as the requirement of the user
.
Class is an user define data type which is used to create new data type as the requirement ofthe user by encapsulating different standard data type or other user define data type in a
single unit.
It is also possible to say that common name of set of object is called class. alternately we can
say that class is the blue print or logical design of object in the encapsulated form of
instance variable and methods so in class methods and variable are present with there
appropriate type . In java 4 types of visibility are present and they are applied in class indesign time. It is also known to us that the method are common for a set of object so all
method should be public.
1. Private : Private visibility specifies that this section can not be access directly from theout side of the object but can be access from any where of object. That means private section
can be access from public, friendly and protected section of the object .So finally we can say
that private section is visible in a single object at a time. Private section is not inheritable.
That means function and variable present in the private section.
2. Deffoult/Friendelly : The default visibility is friendly in java. The default section can beaccess directly from the out side of the object. That means the default section can be access
in entire program of a particular package (Collection of related class). Default section can
be inherited into the subclass. That means variable and function present in the default
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section. Default section can be override and overwrite in the subclass default section can
contains instance variable as well as methods.
3. Protected : The protected section can also be access directly from the out side of the
object. That means the protected is visible in entire program in a particular package sameas default. We know that the default section can not be access in another package but
protected section can be access other package in subclass. protected section can not be
access in non subclass in other package protected section can contains methods as well as
instance variable protected can be inherit into sub class and the method and instance
variable can be overwrite and override in the subclass . To protect overwriting and
overriding the final keyword are used before the visibility of function and variable.
4. Public : The most visibility in java program is public. The public visibilities specify thatthis section can be access from any where in java programming. Public section can directly
access from out side of object. That means public section is visible in the entire program ina particular package public section can also be visible in subclass as well as in non subclass
in other package. Public section can be Inherit in subclass and can be modified as the
requirement of the user. The common name of set of object is called class. It is also possible
to say that class is the blue print or logical design and imaginary design of object.
alternately be can say that class is an user define data type to create new data type by
encapsulating standard data type or other user define data type with there associated
member function (methods) in a single unit as there requirement of the user.
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Core Java Programming language Theory part only
Encapsulation is a binding process by which instance variable are bind with there associated
method to create a complete object. We know that method are common for a set of object
and they are created at the time of class declaration instance variable allocates there
memory at the time of object creation dynamically at the time of execution after allocation of
memory by the instance variable a link between instance variable and there associated
method. This linking process is called Encapsulation or data binding. Which is perform
dynamically at the time of execution this type of binding is called late binding or run time
binding or execution time binding.
The main purpose of encapsulation is to create a single unit by binding different instance
variable and there function and extra cover is arise around the component of the object and
concurrently the internal component are hidden from out side of the object. So we can say
that encapsulation implemented data binding by providing appropriate access pacifiers to
the component. Alternately we can say that encapsulation is used to implement data
abstraction by hiding all components from out side of the object. Encapsulation creates a
single unit and the unit can move independently from one location to another location.
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Core Java Programming language Theory part only
One of the most important features of any programming language is the reusability of code.
Inheritance is process to implement the concept reusability of code. In java three techniques
are used to implement the concept of reusability as:-
1. Function.
2. Inheritance.
3. Package.
Inheritance is a process by which we can create new classes using existing sub class is called
super class and the new class is called base class. Alternately we can say that inheritance is
a process to implement the concept of parent child relationship that means in java more
than one super class can not be present for a single subclass. That means more than one
super class can not inherit into a single subclass so multiple as well as hybrid inheritance
can not be implemented in java. The main purpose of is to reuse the existing code present in
super class in subclass the following advantage are present in inheritance.
Usese
1. Using interface existing code can be reuse in subclass so using the concept of
inheritance programmers can develop large program very easily.
2. Since code can be reuse in subclass productivity of programs is increase.
3. If productivity is increase than the product cost will we decrease as well as
maintenance cost also is decrease.
4. If product cost and maintenance cost is minimum of a product than the
acceptability of the product will be maximum.
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Type of inheritance
Single or simple inheritance :Single or simple inheritance is those type of inheritance in
which a single super class is used to create single subclass. Inheritance visibility ofcomponent can not be change in java graphically we can represent single/simple
inheritance as.
Multilevel inheritance :Multilevel inheritance is those type of inheritance in which a subclass is used as a super class to create another sub class .alternately we can say that
multilevel inheritance is the representation of single inheritance. Graphically we can
represent multilevel inheritance as.
INHERETANCE
SINGLE/SIMPLE
MULTILEVEL
HERERICAL/TREE STRUCTRE
CLASS A
CLASS B
CLASS A
CLASS B
CLASS C
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Hierarchical/Tree structure inheritance : Hierarchical or tree structure inheritance isthose type of inheritance in which every subclass has only one super class. But every super
class can be more than one sub class. graphically we can represent heretical/ tree structure
inheritance as-
In inheritance the concept of overwriting and overriding is arise if an instance variable is
inherit from super class to subclass than in subclass new value can be supplied to the
variable . the new overwrites the executing value of the variable .in the variable the concept
of overwriting is implemented . If user wants to restrict the overwriting than the final
keyword is used before the general declaration of the variable. The final variable can notcan not be overwrite in the subclass . That means final keyword create constant that values
can not be changed in subclass. Function present in subclass can be inherited into subclass
and new definition of the function can be created by the user in sub classes. the new
definition of the function of subclass overwrite the executing definition of function in super
class in subclass new definition is active and in super class the old definition is user want to
protect function overwriting than the final keyword is used before the general definition of
the function . The final keyword can not restrict the inheritance of the method and instance
variable it only restrict only overwriting and overriding.
If class is final than class can not be inherit into subclass the final keyword protect theextension of class in java subclass is the extension of the super class and so final keyword
restrict the extension.
A
BC
D E
F G
H
I J K L M
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Abstract class : Abstract class is that type of the class which has no capacity to create object.Abstract class must be inherit into subclass to create existence of the abstract class. Abstract
class is used as a super class in inheritance.
Abstract Function : Abstract function is that type of function which has no definition orbody, if a class contains an abstract function than the class must be also an abstract.
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The general meaning of polymorphism is single interface multiple task. That means same thing
different form. Poly means many and morph means form. That means polymorphism is those
type of programming concept in which a particular function can take different form by
taking different number of argument and different types of argument and can perform
different task according to the form of the function. In java, polymorphism is only
implemented using the concept of function overloading. There is no concept of operator
overloading in JAVA. In real life different task are performed using a single function by
supplying different arguments. to implement this concept in programming language the
concept of function overloading is arise. The main purpose of polymorphism is to handle
huge number of function.
Function overloading is those type of programming system in which a particular function can
take a different form by taking different number of arguments and different types of
argument and can perform different task according to the form of the function. In JAVA
function overloading is implemented using dynamic binding. Function overloading using
early binding is not present using the concept of simple methods. Function overloading
using early binding can be implemented in JAVA using the concept of static function.
We know that functions are common for a set of object and they are allocate there respective
memory at the time of class declaration. In JAVA objects are created at the time of execution
usingnew operator. After that a binding process is performed between instance variables
and there associated functions. This type of binding is calledlate bindingordynamic
bindingorrun time bindingorexecution time binding.In JAVA generally methods are
banded with instance variables using dynamic binding. So using simple methods, function
overloading can be implemented using dynamic binding. Static function is called using the
class name not the object of the class and can perform any operation on any type of instance
variables using static function. Function overloading can also implement using early
binding.
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Core Java Programming language Theory part only
JAVA programming language is platform independent. That means JAVA program can be
executed on any operating system and on any computer with any internal architecture
(configuration) provided the word length of the computer must be greater than or equal to16
bit.Platform independent indicates that the program is not dependent on the operating
system as well as internal architecture of the computers. JAVA program is not dependent on
operating system of the computer as well as internal architecture of the computer system.
But to execute the JAVA program the internal configuration is a matter, because the word
length of the computer must be greater then or equal to 16 bit.Lessthen 16 bitcomputer isnot capable to execute the JAVA program. The main cause of platform independent of JAVA
programming language is theJVM(Java Virtual Machine).
JVMis anoperating system over the actual operating system.JVMis responsible to make
compressibilityof the actual operating system with the JAVA program.JVMis interfacing
between the actual operating system and the JAVA program. The internal coding system of
JVMis Unicode, which is a 16 bitcoding system. So the interact number of all popular
operating system is present inJVM, which can make a link with the physical operating
system.
JVMis divided in three parts
(1) JIT (Just In time Compiler)
(2) JAVA interpreter
(3) JAVA Run Time Environment
JAVA compiler is known as just in time compiler because all programs are just in time
compiler because the entire program is not converted at a time to its equivalent object code
(byte code). We know that compiler compile a program in to two phases. The first phase is
known as analysis of source program. In this phase only syntax errors are checked. If syntaxerrors are present then appropriate error message is displayed. The second phase is called
synthesis of object program. In this phase actual object code is created. But JAVA compiler,
compile those segment which is to be executed in the next cycling.
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JAVA compiler is not compile system defined function because they are in compiled form. That
means JAVA compiler compile a particular segment at a time which is to be executed in the
next cycling. JAVA compiler creates an intermediate code which is called byte code, written
in Unicode system. The intermediate byte code is interpreted by the JAVA interpreter and
creates appropriate object code understandable by the physical operating system. The JAVAcompiler is javacand the JAVA interpreter is java. JAVA interpreter interprets byte
code to its equivalent object code and sent to the java run time environment and the java run
time environment sent the interpreted object code to the operating system. Actually the
operating system and the java interpreter is interfaced using java runtime environment. The
main component present behind the platform independency is the java runtime environment.
In this component all the kernel information of popular operating system are present at the
time of installation. The kernel information is activated in the java runtime environment
which is present in the internal operating system of the computer. The other kernels are
temporarily deactivated.
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MULTITHREADINGMultithreading is those type of programming concept which is used to implement the concept of
multitasking. Thread means, small program which can be executed at a time. Multithreading
means more then one smalls program which are executed simultaneously not concurrently
using small span of time and using the round robin scheduling. We know thatJVMis an
operating system over the operating system, so in JVM a scheduler is present which is
responsible to implement multithreading. In multithreading threads are differentstates :-
1. New born state
2. Ready state
3. Running state
4. Suspended state (temporarily)
5. Terminated state or killed
In JAVA a thread class is present which is used to implement the concept of multithreading. A
run( ) function is present in the thread class which is used to run a thread. An init( )
function is present, which is used to initialize a thread or new born thread is created.Start( ) function is also present, which is used to ready a thread to execute.Stop( ) function
is present which is responsible to terminate a thread. For temporarily suspended of thread
three functions are present and they are-
1. Sleep
2. Suspended
3. Wait
The sleep( ) is automatically deactivated after specific time given in millisecond in the sleep( )function. The suspended( ) function is deactivated when a resume( ) function is called. Wait
function is deactivated when a notify( ) is called.
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Constructor is a special member function thats name is same with class name and that isautomatically invoked at the time of object creation. Construction has no return type even
void. Construction can take argument or can not be. Constructor can not be declared in the
private section of the class. But other visibility can be present with constructor. That means,
constructor can be public, protected or friendly but can not be private. Constructor is
divided in to two categories according to the argument. If the constructor can not take any
argument then the constructor is called default constructor. If the constructor can take any
argument then it is called parameterized constructor. If a class contains a parameterized
constructor then the class should also contains a default constructor. There is no concept of
copy constructor in JAVA. Constructor can not be inherit in the derived classes but can beinvoked from the sub-classes using the keywordsuper. If the super class contains a
default constructor then it is not necessary to present a constructor in the sub-classes. If the
super class contains a parameterized constructor, then in the sub class minimum one
constructor must be present, to invoke the super class constructor. A single class can
contain more then one constructor. That means constructor can be overloaded.
There is no concept of destructor in JAVA. The concept of garbage collection deletes all the
variables and functions of the program thats execution is completed. So all the instance
variables are automatically initialized with there zero values at the time of creation of the
object, because the memory is cleared by the garbage collection concept. If user wants to
delete an object from the memory then thefinalize( ) function can be used to perform thosetype of operation. That means, using finalize () function, particular object can be deleted as
the choice of the user but by the garbage collection all the objects are deleted after
execution of the program which is performed automatically by theJVM.
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Generic programming is those type of programming concept by which we can create type
independent code for all the type which maintains same algorithms. In JAVA programming
language large number of generic classes is present to implement any type of concept.
Generally the generic classes are vector, stack, queue, array list, circular queue, B tree etc.
In JAVA the concept of generic functions is not present, only the concept of generic classes
is present. Using this class user can handle any type of element as the requirement of the
user.
For example :- array is a generic class to handle any types of values using the concept of array.The array class contains a large number of methods to handle array elements. Thefill
function is used to store values into the array. The sorfunction is used to arrange data
elements in ascending or descending order. The delete function is used to erase data
elements from the array. Similarly the search function is used to test existence of a
particular element.
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Exceptions are a type of error besides then the syntax error or logical error as divide by zero.Alternately we can say that those types of error which are not belonging to syntax error or
logical error are calledEXCEPTION. Exceptions are divide in to two categories :-
1. Synchronous or software related exception.
2. Asynchronous or hardware related exception.
A synchronous type of exception is also called software exception. Which are arise due to
software limitation, like arithmetic exception, input/output exception, number format
exception etc. synchronous exceptions can be smoothly handled by JAVA programming
language, because huge number system defined exception classes are present. The popularexceptions classes are input/output exception, arithmetic exception, number format
exception, array index out of bound exceptions, string index out of bounds exception, class
not found exception, sql exception etc. using system defined exception classes any type of
exception can be handled besides then the system defined exception. User can also create
his own exception classes to handle exceptions. In JAVA programming the following tools
are used to handle exceptions.
1. Try ( )
2. Catch ( )
3. Throw ( ) /Throws ( )
The try block is used to identify exception. After identifying the exception JAVA automatically
throws the exception to appropriate catch block, if the exceptions are system defined
exception. If the exceptions are user defined exceptions then the throw statement is used to
throw the exception to appropriate catch block. A single function can contain more then one
try block and correspondingly more then one catch block. It is also possible to present more
then one catch block corresponding to a single try block.
Asynchronous exceptions are those types of exceptions which are arises due to hardware
failure, which can not be handled by the JAVA programming language. Asynchronousexceptions can not be handled by any programming language.
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We know that methods are common for a set of object and instance variables are distinct for
every object. Methods are allocated their memory at the time of class declaration and
instance variables are allocated their memory at the time of object creation. In JAVAprogramming language objects are allocated their memory at the time of execution using
the new operator. After allocation of memory the instance variables are binds with their
associated methods at the time of execution. This type of data binding is also calleddynamic
bindingorlate bindingorexecution time bindingorrun time binding. In JAVA object can
not allocate their memory statically at the time of compilation. They allocate their memory
at the time of execution. So only dynamic binding is present in JAVA. The concept of static
binding is partially implemented using the concept of static variables and static function.
Which are allocate their memory at the time of compilation and can be executed without
object. The concept of dynamic binding is present in JAVA due to JAVA supports distributed
processing. In distributed processing a large program can be decomposed to its smallersegments and distributed among all the processors which are connected with the server or
main computer.
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Distributed processing is that type of processing in which more then one processor are involvedto execute a single program segment wise concurrently. In distributed processing a large
program is divided to its independent smaller segment and processed by the processor,
which are connected with the main server. All the segments are executed concurrently and
at the end all the segments are combined and produce the actual output on the main server.
The processing speed is rapidly increased due to the concept of distributed processing. To
implement the concept of distributed processing the system should be in network. In JAVA
programming language the distributed processing is implemented. Using the concept of
applet andRMI(Remote Method Invocation) and using the concept of socket
programming.
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We know that JAVA programming language is the combined form ofCandC++. The syntax cal
concept of JAVA is arising from the C language. We know that the syntax of C programming
language is very simple. This simplicity of syntax is arising in the JAVA programming
language from the C language. The conceptual framework of JAVA is arising from C++,
which are very simple concept. So the JAVA programming language is syntaxically and
conceptually very simple.
JAVA programming language provided high security to its data members and data values. We
know that JAVA is a pure object oriented programming language. So, all the components
must be present within class. We also know that classes are always encapsulated, so objects
are always encapsulated. A cover is present around the components of objects, so any
component can not be directly accessed.
The visibility layer of JAVA programming like private, friendly, protected etc provides securityof the components. Inheritance and the concept of the package also increase the security of
instance variables and methods. The applet programming can be executed on any web
browser and can not perform any operation on the terminal on which it is executed. So,
using the concept of applet information can be propagated in the entire network with
affecting the network.
User can developed any type of application using JAVA programming language. So we can say
that JAVA is the most powerful programming language. JAVA language also has the
capability to access native programming languages C, C++ etc as the choice of the user.
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The most important component of JAVA programming language isJVM (Java Virtual
Machine).JVM is divided in three components-
1. Java Compiler
2. Java Interpreter
3. Java Runtime Environment
The JAVA compiler is responsible for to compile a source program to its equivalent
intermediate code byte code, which is written in 16 bitcoding system Unicode. The byte
code is understandable by any computer after interpreting to equivalent object code. The
JAVA compiler compiles a JAVA program using two phase. The first phase is the analysis of
source program in which syntax errors are checked. The next phase is the synthesis of objectprogram in which actual byte code equivalent is generated. JAVA compiler not compiles the
system defined function, because they are in compiled form. The compiler is not compiled
the whole program at a time, if the program is very large and divided by modules. Module
by module compilation is performed by the JAVA compiler. It is also calledjust in time
(JIT) Compiler.
The next phase of execution of JAVA program is interpretation of byte code performed by JAVA
interpreter(JAVA). The JAVA interpreter interprets the byte code to its equivalent object
code understandable by the physical operating system and transfer to the JAVA run timeenvironment. That means JAVA program is executed in two phases-
1. Compilation
2. Interpretation
So JAVA is compiled and interpreted.
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The full form of applet is application layout. Applet is stand alone program which can be
executed independently in any computer by using any web-browser like hot java, internet
explorer, MSN messenger etc. applet program is stand alone program in which main
function is not present and can be propagated in the internet automatically. System defined
applet, class applet and j applet are present in the package appletjava andjavax. Applet
program can not be created without the system defined class appletandj applet. The classes
must be inherit in the user class to create applet program. The applet class generally
contains the following popular functions:-
1. start
2. init3. paint
4. repaint
5. destroy
The start( ) function start the execution of an applet program which is automatically called. The
init( ) function initialize the applet to set the frame and visible the frame in the applet viewer
and applet window. Thepaint ( ) function actually perform operation on the applet window
as well as applet frame. The repaint( ) function is used to called the paint function again.
The destroy( ) function kills the applet and stop viewing.Applet is divided in two categories according to the storage or location of the applet:-
1. Local applet
2. Remote applet
Local applets are those types of applets which are stored in the same computer on which they
are executing. If the system is stand alone, system can not connected in the network. User
can create only local applet on that computer. Remote applets are those types of applets
which are stored in the server and executing in any computer connected with the server.Generally websites are contains remote applet.
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JAVA programming language is basically used to design the interface. JAVA is generally used
as a front end program (software) in application development. JAVA programminglanguage has the capability to interact with anyDBMSorRDBMS. To store data values
using the security layers of the DBMS. JAVA programming language has no such powerful
capability to store data values in the files with maximum security. JAVA data file can be
opened and modified by any user very easily but we know that in DBMS as well as RDBMS
provides high security to the database using user name, password, privilege and rolls. So
JAVA programmers are generally stored data values in data bases in theRDBMS, using the
JAVA application program interface (A.P.I) JDBC (Java database connection).using
JDBCuser can access andRDBMSandDBMSsuch as oracle, SQL server, MS access,
Visual FoxPro etc as the choice of the user by selecting appropriate driver and set a
connection with the databases. That means, JAVA API (Application Program interface)
programs are present to interact with other programming languages as the choice of the
user.
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One of the most important features of any programming language is to implement the concept
of object re-use ability. In JAVA programming language has the capability to re-use existingcode in other programs or in same programs. If an existing code is to be re-used in other
program then the concept of package is arise. Package is the collection of related classes
which is used to re-use existing code in other programs. JAVA programming language has
huge number system defined packages. Which are contains system defined functions in
appropriate classes. In JAVA programming language, near about162 System defined
package are present and near about18000 System defined functions are present.
The most popular System defined packages are applet, lang, util, swing, net, javax, awt etc.
User can create his own package as the choice of the user. Package generally contains
public classes otherwise the class can not visible in other program. The package statementmust be the first statement in the any user program. After that any statement can be present.
User must be create a subdirectory as same as the package name and the program must be
in the subdirectory with the name of the public class name with.(Dot) java extension. The
class file of the program must be saved under the subdirectory. The package can be import
in the super directory only. So, program in which the package is re-used should be created
in the super directory of the package directory. At a time only one public class can be stored
in a package. If the class is not public then it can not be import in the user program. Non
public classes are hidden from the user program and they can not be accessed in the user
program.
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7/30/2019 Java Color
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Core Java Programming language Theory part only
In JAVA programming language the concept of multiple inheritance is not present because
more then one sub class can not be inherit at a time in a single sub class but more then one
interface can be inherit in to a single sub class. That means using interface the concept of
multiple inheritance can be implemented.
Interface is also is an user defined data type as same as class. In which only constant value and
abstract functions can be present. In interface the default visibility is public. Interface can
contains function but all the functions are abstract by default. Functions present in the
interface must be redefined in the sub classes otherwise error will arise. Data member
present in the interface are by default static final. That means, only constant value can bepresent in interface. We can not change the data members in the sub classes of the interface.
An interface can be inherit in to another interface using the keywordextends but more then
one interface can not be inherit to a single interface at a time. An interface can be inherit in
to a sub class using the keywordimplements.More then one interface can be inherit in to a
sub class at a time. A system defined package event underawtpackage is present which
contains all the system defined interfaces asActionListener, KeyListener, MouseListener,
mousewheelListener, ItemListener, Componentlistener, WindowsListeneretc.
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